Some builds use the Thompson foregrip bracket to mount the Spas, others use a metal block.
Check out the following threads on the Aliens Legacy. They all have different approaches to attaching various parts:
The Aliens Legacy is a global community for fans of the Alien film series. The discussion of the Alien series of films and the props used in them is the aim, but if it's got Big Bugs and Big Guns, then they are welcome too!
forum.alienslegacy.com
The Aliens Legacy is a global community for fans of the Alien film series. The discussion of the Alien series of films and the props used in them is the aim, but if it's got Big Bugs and Big Guns, then they are welcome too!
forum.alienslegacy.com
The Aliens Legacy is a global community for fans of the Alien film series. The discussion of the Alien series of films and the props used in them is the aim, but if it's got Big Bugs and Big Guns, then they are welcome too!
forum.alienslegacy.com
The 'half hexagon' parts I am not sure of their function (I am hardly an expert on the Pulse Rifle, there are many around who know far more than I do). On my black PR, they are molded as part of the shroud, but on the Matrix, I think that they are plates.
The plates on the front and rear of the magazine well are normally done in the same colour as the shroud. They are support plates to keep the bottom of the shroud together. Some builds that I have seen also have an extra plate on the front and rear of the carry handle/sight as well.
Spas pump grip is synthetic, replica ones can be resin or plastic, depending on the source.